In recent years, automotive component manufacturer's use of autodeposited coatings has dramatically increased due to the performance, cost-effectiveness, versatility and environmental advantages that this technology offers. Although historically used to coat only steel substrates, the increased use of zinc and zinc alloy coatings presents further market opportunity for autodeposition of coatings.
Due to differences in chemical reactivity between steel and zinc, obtaining high quality coatings by acidic chemical deposition (autodeposition) has required some process development innovations. In this paper, the procedure of coating deposition on galvanized surfaces is described and compared to the deposition on steel. Corrosion performance of autodeposited coatings on galvanized steel is evaluated by a cyclic corrosion test and compared to the performance of another widely used coating for galvanized substrates.
THE INCREASING CORROSION protection performance requirements demanded of automotive components have resulted in greater use of galvanized or galvannealed steel for these parts. Although the autodeposition process has long been used for the coating of cold- or hot-rolled steel, simultaneous application to steel and zinc is problematic due to the different reactivity of the metals1.
The recent development of an autodeposition process improvement that enables simultaneous coating of steel and galvanized steel has allowed autodeposition technology to address this growing market. Furthermore, this new coating process maintains the environmental attractiveness and operating advantages inherent to autodeposition.
This paper describes the autodeposition process and examines the corrosion performance of autodeposition coatings over a variety of substrates in a cyclic corrosion test. Comparison is made to the performance of a standard finishing system used in the automotive component market.